With a display panel such as a liquid crystal panel or an organic EL panel, in general, display unevenness sometimes occurs due to variations in machining accuracy in a manufacturing step. Accordingly, before the display panel is shipped, an inspection for detecting display unevenness of the display panel is performed.
In the inspection, the pixels of the display panel are illuminated, the pixels are imaged using a camera including a solid-state image sensor so as to measure the luminance of the pixels, and thereby display unevenness is detected. The detected display unevenness is corrected, whereby an improvement in the quality of the display panel is achieved.
On the other hand, the solid-state image sensor of the camera varies in sensitivity, and furthermore, the amount of light received by the solid-state image sensor through the lens of the camera tends to be smaller if it is received from the peripheral portions of the lens in comparison to being received from the central portion of the lens, and thus a difference in brightness occurs between the central portion and the peripheral portion.
In this way, if there is variation in the sensitivity of the solid-state image sensor in the camera that performs the inspection and the amount of light received by the solid-state image sensor via the lens differs between elements, even if there is no defect in the display panel that is to be inspected, unevenness that does not actually exist in the display panel is imaged in the captured image of the display panel imaged by the camera and it is not possible to obtain a correct inspection result for the display panel in some cases.
As a countermeasure against this, Patent Document 1 discloses a captured image calibration method that aims to calibrate a captured image of a display panel that is an inspection target object, based on a calibration coefficient for calibrating sensitivity variations or the like of a solid-state image sensor.
According to the captured image calibration method in Patent Document 1, sample light emitted from an emission window of an integration sphere provided with a light source is imaged with the camera, and a calibration coefficient is created based on the imaged data of the imaged sample light. The captured image of the display panel that is the inspection target object is calibrated based on the calibration coefficient.
The integration sphere used in this calibration method has a hollow sphere body with an inner surface on which a diffuse reflection material is applied, the light emitted by a light source is reflected by the diffuse reflection material in the sphere body, and the sample light is emitted with a uniform luminance distribution from the emission window of the integration sphere to the surface of the emission window.
In this way, with the captured image calibration method of Patent Document 1, it is possible to create a calibration coefficient based on data obtained by imaging sample light having a uniform luminance distribution on the surface of the emission window, and the captured image obtained by imaging the display panel that is the inspection target can be calibrated based on the created calibration coefficient.